net: usb: lan78xx: Use generic_handle_irq_safe().

Instead of manually disabling interrupts before invoking use
generic_handle_irq_safe() which can be invoked with enabled and disabled
interrupts.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Woojung Huh <woojung.huh@microchip.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: UNGLinuxDriver@microchip.com
Link: https://lore.kernel.org/r/20220211181500.1856198-7-bigeasy@linutronix.de